1. Field of the Invention
The present invention relates to a detection method of a digital radio communication apparatus and a circuit thereof, and, in particular, to a detection method of a digital radio communication apparatus, which receives a PSK (Phase Shift Keying) modulated signal, and a circuit thereof.
2. Descriptions of the Related Art
FIG. 1 shows a block diagram of an example of a detection circuit of a digital radio communication apparatus in the related art. In the figure, for example, an intermediate frequency (IF) signal of a PSK modulated signal, which the digital radio communication apparatus has received, is supplied to a quantization circuit 11 via a terminal 10. The quantization circuit 11 quantizes the phases of the intermediate frequency signal and supplies, to a sampling circuit 12, quantized phase data, shown in FIG. 2A, obtained from quantization of the phases of the received intermediate frequency signal. To the sampling circuit, a reproduction clock signal shown in FIG. 2B is also supplied from a PLL (Phase Locked Loop) 13. The sampling circuit 12 samples the quantized phase data at each rising edge of the reproduction clock signal, and supplies, to the PLL 13 and a data determination circuit 14, the sampled quantized phase data, shown in FIG. 2C.
The PLL 13 generates the reproduction clock signal which is in synchronization with the sampled quantized phase data. The data determination circuit 14 determines data of a plurality of bits, from the sampled phase quantized data, in accordance with the phase, thus, performing PSK demodulation (or detection), and outputs thus-obtained data via a terminal 15.
In this circuit in the related art, the quantized phase data is sampled at one sampling point during each period of the reproduction clock signal, and the sampled quantized phase data is used for the data determination. Therefore, when a sudden phase deviation occurs at a sampling point, the data determination may be erroneously performed.
Further, in a method in which a limiter is provided at a preceding stage so that the amplitudes are limited and only the phases are used for reproduction, the opening point of each eye pattern is narrow in comparison to the case where the limiter is not provided. Therefore, each sampling point determined by the reproduction clock signal should be strictly determined. When a sampling point deviates even a small amount forward or backward, good detection cannot be performed. Further, due to an insufficient receiving ability of the digital radio communication apparatus or spurious interference occurring inside the apparatus, the eye pattern is blurry. Thereby, good detection cannot be performed, and data determination may be erroneously performed.